The present invention generally relates to fabrication methods and resulting structures for semiconductor devices, and more specifically, to gate-all-around FETs having uniform threshold voltage.
The MOSFET is a transistor used for amplifying or switching electronic signals. The MOSFET has a source, a drain, and a metal gate electrode. The metal gate is electrically insulated from the main semiconductor n-channel or p-channel by a thin layer of insulating material, for example, silicon dioxide or glass, which makes the input resistance of the MOSFET relatively high. The gate voltage controls whether the current path from the source to the drain is an open circuit (“off”) or a resistive path (“on”).
N-type field effect transistors (NFET) and P-type field effect transistors (PFET) are two types of complementary MOSFETs. The NFET includes n-doped source and drain junctions and uses electrons as the current carriers. The PFET includes p-doped source and drain junctions and uses holes as the current carriers.
The nanowire or nanosheet MOSFET is a type of MOSFET that uses multiple stacked nanowires/nanosheets to form multiple channel regions. The gate regions of a nanosheet MOSFET are formed by wrapping gate stack materials around the multiple nanowire/nanosheet channels. This configuration is known as a gate-all-around (GAA) FET structure. The nanowire/nanosheet MOSFET device mitigates the effects of short channels and reduces drain-induced barrier lowering.